Process for the purification of crude phthalic anhydrid.



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specification of Letters Patent.

BIA, PENNSYLVW, C1800, CALIFOBNIM a ran an runrrrcn'rron or canon surname Patented a t. 22f. iaia.

Application filed June as, me. serial No. eraser.

man man run act or mason a, was, 22 arm. 1., eat.

To all whom it may concern."

Be it known that we, COURTNEY Conovrm and HARRY D. GIBBS, citizens of the United States of America, residin in the city of Philadelphia, county of Philadelphia, State of Pennsylvania, and in the city of San Francisco, county of San Francisco, State of (whose post-oflice address is Washington, D. C.,) have invented a new and useful Process for the Purification of Crude Phthalic Anhydrid, of Whlch the following is a specification.

This application is made under the act of March 3,1883, chapter 143 (22 Stat, L. 625) and the invention herein described and claimed may be used by the Government of the Government,

the United States or any of its ofiicers or employees in the prosecution of work for or any person in the United States, without payment to us of an royalty thereon.

ur invention relates to a process for the purification of phthalic anhydrid.

It is well known that phthallc anhydrid, substantially pure, is commonly produced by the sublimation of crude or impure phthalic anhydrid or phthalic acid. This rocess is expensive and often results in loss of thephthalic anhydrid. The object of our invention is to provide a process which shall be inexpensive, shall result in little loss of valuable products, from other objectionable features of the processes employed at present.

Our invention consists in substance in the pure phthalic anhydrid by dissolving the crude or impure anhydrid in a non-aqueous solvent at a temperature somewhat above ordinary room temperature, filtering out such impurities as are insoluble, decolorizing the solution obtained by means of a substance capable of adsorbing color from non aqueous solution, crystallizing out phthalic anhydrid by lowering the temperature of the solution, crystalllzmg out phthalic anhydrid mixed with the accompanying impurities by again lowering the tem rature, and later separating most of the impurities practicall free from phthalic anhydrid by further re notions of temperature. y v

To illustrate the practical operation of our proeem' we shall describe in detail the and which shall be free preferred procedure. Crude phthalic anhydrid containing such impurities as are commonly present, includin highly colored compounds, naphthalene su fonic acids and naphthalene, is dissolved in carbon tetrachlorid which has previously been used in this process and which contains small quantitles of the impurities in solution. The solution is brought about at a temperature between and 7 0 Centigrade, the preferred temperature being about 70. The solution is brought about in a tank of such design and with such connections and accessories that its contents may be held at the desired temperature (70), that the solvent may be passed into it continuously, that the solution leaving it must pass through a filter, and that it may be opened to receive successive charges of crude phthalic anhydrid or for the removal oi: material from the filter. More than one of these tanks connected in series are rused for dissolving the crude material.

The warm solution of phthalic anhydrid and accompanying impurities 'is passed through another series of tanks substantially like the .ones used for solution and which are kept at about 70 centigrade. These tanks each contain a charge of decolorizing charcoal to adsorb the color from the carbon tetrachlorid solution.

The carbon tetrachlorid solution, nearly decolorized, is next passed through a series of tanks substantially the same as those used for solution and for decolorizing, but of -such design and with such accessories that so aduated that the crystals formed at the big est temperatures are practically pure phthalic anhydrid, while the crystals or precipitated masses formed at the lowest temperatures consist of "the impurities practical%% free from phthalic anhydrid.

e purest crystals of phthalic anhydrid purities is used are removed, and washed if necessary with cold carbon tetrachlorid. The crystal masses which contain phthalic anhydrid to gether with substantial quantities of impurities are returned to the beginning of the process and worked up with the crude material. The precipitated masses which are practically free-from phthalic anhydrid are not again introduced mtothe process. The mother liquor, consisting of carbon tetrachlorid containing small proportions of imagain as a solvent for the crude phthalic anhydrid. I v

We[have discovered that the process as above'described may bevaried in man ways and ;-yet will-produce phthalic anhy rid of high purity. Thus,-other non-aqueous $01 vents such as petroleum distillates (gasolene, kerosene, or other sol-vent having a desired boiling point) acetone, benzene, carbon disulfid, and chloroform, may be substituted wholly or in art for the carbon tetrachlorid, except that t e temperatures for solution, decolorization, and crystallization must be varied somewhat. One advantage in the use of petroleum distillates or carbon disulfid' is ing the temperature, separating out the im that these solventsdissolve less color from may be' substituted wholly or in part for the of concentrating the solutions or obtaininga purer solvent for the crude phthalic anhydrid.

Having thus described our. invention, we

claim I .1. A process for the purification of phthalic anhydrid, .which rocess consistsin treating phthalic anhydnd and the sub-v stances which commonly accompany it in the crude state with a non-aqueous solvent, at a temperature above 30 vcentigrade, filtering, treating the solution with a substance capa-.

color from non a'queous so-- blc of adsorbihg 1utions,-crystall1zing phthalic anhydrid from the partia ly decolorized solution by lowerthe tem era-' purities by further .loweri i'quoragain to 'ture, and using the mother dissolve the crude material.

--2. A process for the purification of phthalic anhydrid, which process consists in treatin p stances w 'ch commonl the crude state with car a; temperature above 30 accompany it in n tetrachlorid, at cent1e,"filtering the temperature,

thalic anhydnd and the sub? menses ing, treating the solution with'a substance capable of adsorbing color from carbon tetrachlorid, crystalliz'ing phthalic anhydrid from the partially decoloriaed solution by lowering the temperature, separating out the impuritles by further lowering the parature and using the mother liquor-again to dissolve the crude material.

3. A process for the phthalic anhydrid,

which process consists in purification of i treating phthalic anhydrid and the substances which commonly accompany it inthe crude State h a non-aqueous solvent, at 'a-i perature above 30 centigrade, treatingthe solution with a substance capable of adsorbing color from non-aqueous solutions, crystallizing phthalic anhyditid from the .par-. i

Itially decolorized solution by lowering the temperature, separatih'g-out the impurities by further lowering the temperature, and

using the mother liquor again to dissolve the crude material.

4. A phthalic anhydrid, which process consists in treating phthalic anhydrid and the'substances which commonly accompany it in the crude process for the purification of state with a non-aqueous solvent at a. temperature above 30 centigrade, filtering, treating the solution with decolorizin char- .coal, crystallizing phthalic anhydri from the partially decolor'ized I separating out the impurities by further lowerin the temperature, and using the mother 'quor aga n to dissolyethe crude material.

5. phthalic a'nhydrid, which in treating phthalic anhydrid and the substances. which commonly crude state with a non-aqueous solvent, at

a temperature above 30. centiggde, crystalm the solution by lowering the- -temperature, separatlizing the phthalic anhydrid ing out the impurities by further lowering the temperature, and usingthe mother liquor again to dissolve the crude material.

solution by loweraccompany it inthe.

6 A process 'for the purification of phthalic anhydrid, which process in I treating phthalic anhydrid and thesub- Y stances which commonly accompany'it in. the-crude state with,a

ata temperature above 30 centigrade, filter ing, treating. the. solution capable of adsorbing color from non-aqueous solutions, crystallizing phthalic anhydrid from the partially decolonzed solution, separating out theimpuritiesiby the solvent away from the im urities, and

the distillate again to lve the crude material.

.7. A process for the purification of crude phthalic anhydrid, which process consists in.

non-aqueous solvent,

with a'subst'auce treating phthalic anhydrid and the substances which commonly accompan it in the crude state, with carbon tetra-chi orid at a term- I process for the (purification of rocess consistsv ature above 30 ion with decolorizing charcoal, crystalfrom the partially lowering the temphthalic anhydr-id from the solution by the temperature, hthalic anhydrid to the beto be worked up with 0., filtering, treating the lizing phthalic anhydrid decolorized solution by perature, crystallizing mixed with impurities further lowering ing this impure p ginning of the process the crude product, separating impurities from the mother liquor by again lowering 1,so1,see

tures in the presence of two subscribing wit- 15 nesses.

COURTNEY GONOVER.

HARRY D. GIBBS.

Witnesses:

JOSEPH A. AMBLER, LAURA A. SK1NNER. 

